1. Field of Invention
The present invention relates generally to improvements to the delivery of drugs, particularly to systems for subcutaneous injection/aspiration (syringes) for drug delivery providing intermittent, episodic or limited drug delivery (as opposed to continuous drug delivery of syringe pumps). More specifically, this invention relates to an improved means of subcutaneous drug (fluid) injection and aspiration, providing a means and method of controlling and monitoring the interaction of specific flow rate and pressure during fluid injection and aspiration with a hypodermic hollow-core needle.
2. Description of the Prior Art
Infusion pumps devices and systems are relatively well known in the medical arts, for use in delivery or dispensing a prescribed medication to a patient. These may be compact pump housings or larger stationary pump housing units. The administration of prescribed drugs has been described in the literature as administration to a patient through infusion tubing and an associated catheter or the like, thereby introducing the drug intravenously. These systems have seen improvements over time with respect to determining infusion line occlusion. Line blockage would cause pressure in the syringe to increase. Systems in the prior art have been developed to identify a predetermined threshold or to monitor pressure to determine means for selecting ranges of occlusion pressures to insure patient safety. U.S. Pat. Nos. 5,295,967; 4,731,058; and 5,080,653 show systems (with syringe pumps or the like) which are adequate for the intended use of intravenous drug delivery and more specifically for monitoring occlusion during infusion. However, these systems do not provide a means for drug delivery subcutaneously via a hypodermic needle. Moreover these systems do not provide a means of aspiration during drug delivery, which is a medical requirement for subcutaneous injection in an attempt to avoid intravascular placement of the hypodermic needle.
Pain, tissue damage and post-op complications have long been tolerated as negative side effects from the use of existing hypodermic drug delivery injection systems. This is well documented in both the dental and medical literature. The pain and tissue damage are as a direct result of uncontrolled flow rate in conjunction with excessive pressures created during the administration of drug solutions within the tissue spaces. Subjective pain response of a patient has been demonstrated to be minimized at specific flow rates during the administration of a drug. Also, it has been scientifically demonstrated that particular pressures (excessive without occlusion, per se) for a specific tissue type will cause damage. It is therefore critical that a specific flow rate in conjunction with a specified pressure range be maintained during the delivery of fluids (drugs) when a subcutaneous injection is given preventing subjective pain response as well as tissue damage. It is also necessary that this system have the capability to aspirate under controlled conditions of rate and pressure to avoid the same negative side effects during fluid movement. U.S. Pat. No. 5,180,371 to Spinello, incorporated herein by reference, presented an invention which allowed a rate to be set for the drug via a hypodermic needle. That invention however did not disclose means of determining, detecting or monitoring pressure during the administration of a drug.
During the early 1980's, several researchers (See for instance Rood, The Pressure Created by Inferior Alveolar Injections, British Dental J. 144:280-282 (1978); Walton and Abbot, Periodontal Ligament Injection; a Clinical Evaluation JADA.(Oct. 1981); Smith and Walton , Periodontal Ligament Injection; Distribution of Injected Solution Oral Surg 55:232-238 (1983)) clearly demonstrated and concluded that the pressure created by the injected fluid is critical to preventing tissue damage and a pain response. Variability, different collagen types and connective tissue densities results in different tissue compliance and distensibility. These variations are found between subjects and within the individual subjects. Rood in his 1978 article states that "[t]he relationship between rate of injection and pressure rise seen clearly with the smaller volumes was lost when 2.0 ml was injected. Several high pressures were recorded and some unexpected low ones. Many tracings showed a pattern suggestive of tissue disruption and it is possible that said low pressures were due to the fluid no longer being contained within the pterygomandible space as the volume injected was similar to the previously estimated volume of the tissue space." Hence, it appears that the rate of flow is not directly related to pressure during an interstitial injection.
Smith and Walton described in their article identified supra discussed above that they have performed a histologic animal study (canines) using a technique to calibrate manual pressures produced. They concluded that the "Volume injected and needle location were not always related to distribution . . . Injecting under moderate to strong back pressure gave deeper and more widespread dye penetration." This once again confirms that pressure is the critical variable in the distribution of the solution within tissues and the volume is not always related to the pressure produced.
Pashley, Nelson & Pashley in "Pressures Created by Dental Injections" (J Dent Res 1981) used a pressure transducer and fixed flow rate created by a motor driven traditional syringe clearly demonstrated that different tissues have a different tissue compliance. Interstitial pressure variability was statistically and clinically significant even with a fixed flow rate. Therefore, it may be concluded that they produced great variations of pressure by using a metered flow rate.
Pertot and Dejou described in their article "Effects of the force developed during periodontal ligament injections in dogs" (Oral Surg. Oral Med, Oral Pathol. 1992) how they used a syringe coupled to a miniature force transducer and found a positive correlation between the number of osteoclasts and the force applied on the syringe plunger, which indicated the pressure generated in the PDL space enhanced osteoclastic activity. This experiment again indicates that pressure is a critical factor to tissue damage and is dependent on the resistance encountered and not the flow rate of the solution into the tissues.
One of the goals of dentistry and medicine should be to administer care to patients in the most humane and painless manner. The sine qua non of any treatment is to produce a desired result without causing damage or pain to the individual. Therefore there is an important need in all fields of surgery for an injection system which can be used to administer a fluid while causing substantially no pain or tissue damage to the patient.